Baseline Urinalysis of the Fully Marine, Herbivorous Dugong (Dugong dugon)

Abstract

The dugong (Dugong dugon) is a fully marine mammal that grazes in nearshore seagrass meadows and whose health is vulnerable to human coastal activities. This study establishes urine baseline ranges for apparently healthy dugongs that can be used as health biomarkers. Voluntary urine samples (uncontaminated by seawater) were collected from 71 wild-caught dugongs in Moreton Bay, Australia, that were held out of water during an annual health assessment from 2008 to 2022. Urine was analysed for qualitative characteristics (colour, turbidity, odour), biochemistry through reactive urinalysis test strips, urine specific gravity (USG) by refractometer, electrolytes by flame photometry, sediment by microscopy, and bacterial culture. Urine of dugongs was typically pale yellow, clear to slightly cloudy, and mildly odorous. Urine was usually slightly alkaline (mean pH 8), and USG was low (mean 1.018). Urinalysis from dipstick indicated consistently negative readings for the presence of glucose, urobilinogen, bilirubin, ketones, and nitrites. Urinary protein was detected in 85% of sampled dugongs. Haemolysed red blood cells were recorded in > 85% of urine samples; microscopy indicated light haematuria (intact red blood cells) in 16% of samples. Seven percent of dugongs had detectable levels of leukocytes suggesting the possibility of mild urinary tract infection. Urinary sediment containing epithelial cells, keratinaceous debris, calcium carbonate crystalluria, and rare struvite crystals were typical. Light to moderate levels of bacteria were present in urine samples, with variable mixed growths, including Halomonas aquamarina, Pseudomonas stutzeri, Photobacterium damselae, Psychrobacter spp., and Staphylococcus aureus. Spermatozoa were present in the urine of 32% of the sexually mature males. Physical characteristics and chemistry of dugong urine showed some similarities to those of manatees and other herbivores. These baseline urinalysis data for healthy wild dugongs in a single population are valuable benchmarks against which dugongs of variable health status (including compromised dugongs) and from other localities may be compared.